Dual power suuply PCB

[dr.power]

Hi guys,

I have designed a PCB for a dual power supply based on both 78xx and 79xx regulator chips.

Plz put your ideas about the layout and the PCB itself (specially the ground plane).
I hope there is not ground loop in y design too.

The input voltage comes from a center taped transformer, the said transformer has two 2200uF caps and two 104 caps to smooth the voltage, thats why I did not use any cap at the input of the below pic.

Furthermore Should I use C1 and C2 in the below pic plz? A guy told me that I should not use them because they cause the regulators to be shorted at the beginning of the start point. What Is your idea plz?
The below regulator will drive a pre-amp based up on Tl074 and the said pre-amp maybe turned on for 24 hours per day.

Thanks a bunch

 

[dr.power]

By the way I can add an extra ground plane around the board edges if needed?

If you would like to know the Clearance of the ground plane at the above PCB is 40mil.

 

[ronsimpson]

There should be a 0.1uf cap on the inputs. The caps with your transformer may be too far away.

 

[4pyros]

You need caps on the outputs of the regulaters too.
The regulaters need heat sinks, what are you going to use?

 

[Brevor]

Like the others have said you should have some caps at the input pins of the regulators. I usually place a tantalum cap on the input and output right at the regulator, sometimes I also put a couple .1 uF SMD caps on the bottom of the board at the regulator. The layout seems OK, But if it were me I would flip the 7805 around so the input and output would not have to cross and you would not have to route the ground around the outside.

 

[bountyhunter]

You can run without heatsink if and only if the max power dissipation does not exceed 1.5W. Otherwise, you need a heatsink. You can get some cheap stamped aluminum kind that can go on with one screw from Digi Key or Fry's.

 

[Boncuk]

How about using something like that?

100nF caps on both, input and output pins of the voltage regulators eliminate the tendency of oscillations (heating the regulator).

A low value output electrolytic cap compensates for possible change of load current.

Schematic and board file contained in file dual-power.zip

Boncuk

 

[bountyhunter]

How about using something like that?

100nF caps on both, input and output pins of the voltage regulators eliminate the tendency of oscillations (heating the regulator).

Funny, the 78XX regs are supposed to be unconditionally stable without external caps. Only time I ever saw one sing in 25 years was if they were driving a reactive load like a DC fan. I realize the data sheet shows the 0.1uF caps, I am not convinced they are required.

I always hang caps on CIN and COUT to improve transient response.

 

[dr.power]

There should be a 0.1uf cap on the inputs. The caps with your transformer may be too far away.

Hi Ron And thanks.

Ok I will reflect this on the PCB...
I think I do not need 1 big electrolyte caps for the input because my transformer has two 2200uF caps. right? Or you think That I need two big electrolyte caps just near the inputs of the regulators as well as the 0.1uf caps?

Kind reagrds.

 

[dr.power]

You need caps on the outputs of the regulates too.
The regulates need heat sinks, what are you going to use?

Thanks sir,
So using two 220uF or 330uF caps on the output of the regulators do not harm the regulator in the long term??

 

[dr.power]

Like the others have said you should have some caps at the input pins of the regulators. I usually place a tantalum cap on the input and output right at the regulator, sometimes I also put a couple .1 uF SMD caps on the bottom of the board at the regulator. The layout seems OK, But if it were me I would flip the 7805 around so the input and output would not have to cross and you would not have to route the ground around the outside.

Thanks.

I do not like to filp one regulator because then I would have some problems by adding a heatsink...

 

[dr.power]

You can run without heatsink if and only if the max power dissipation does not exceed 1.5W. Otherwise, you need a heatsink. You can get some cheap stamped aluminum kind that can go on with one screw from Digi Key or Fry's.

Thanks.
Are you talking about the power dissipation of the output of the redulators? What about voltage drop at the regulator chip itself due to the input volatge? MAkes sense?

 

[dr.power]

How about using something like that?

100nF caps on both, input and output pins of the voltage regulators eliminate the tendency of oscillations (heating the regulator).

A low value output electrolytic cap compensates for possible change of load current.

Schematic and board file contained in file dual-power.zip

Boncuk

Hi Boncuk,

Thanks for the pictures, I can not open teh zip file in protues right?
Your design is good but your pinheaders pad have larger distance to each other when copared to mine, thats why your ground plane is much nicer than mine...
How did you create the screw tracks at the edges of your pcb design plz? and what is the dimentionas and clearance of your design plz?

I will modify my design and add the 0.1uF caps on the input and will let you take a look at it in several other minuts.

 

[bountyhunter]

Thanks.
Are you talking about the power dissipation of the output of the redulators? What about voltage drop at the regulator chip itself due to the input volatge? MAkes sense?

Power dissipation of the regs themselves which is basically (VIN - VOUT) X ILOAD.

 

[dr.power]

Modyfied PCB

Ok heres the new one PCB design which contains the input 104 capacitors.

I have put a read square around the pcb so that ask you guys if it the ground around this red square can generate any ground loop? If so I can remove the outer ground loop.

Thanks

 

[Brevor]

I do not like to filp one regulator because then I would have some problems by adding a heatsink...

There are lots of comprimises in electronics design.

It should be fine, ground loops are not a big problem in a power supply.

 

[Boncuk]

Hi Boncuk,

Thanks for the pictures, I can not open teh zip file in protues right?

Zipped files are compressed files. When unzipping the original files are being restored (in that case the schematic and board files).

Your design is good but your pinheaders pad have larger distance to each other when copared to mine, thats why your ground plane is much nicer than mine...

I used screw head terminals with a pin distance of 5.08mm (0.2")

How did you create the screw tracks at the edges of your pcb design plz? and what is the dimentionas and clearance of your design plz?

I never use Proteus ARES to create a PCB. It has a very limited library for components. Instead I use Eagle.
Proteus ARES should offer a function called "Restrict" or "Keepout". Use the center of the mounting drill hole and draw a circle around it using the "Restrict" layer. The ground pour should then stop at the "border". Clearances are 0.4064mm (0.016"). Board size is 66.5X42.0mm (2.62X1.65")

I will modify my design and add the 0.1uF caps on the input and will let you take a look at it in several other minuts.

Boncuk

 

[dr.power]

Power dissipation of the regs themselves which is basically (VIN - VOUT) X ILOAD.

Thanks, I am wondering how to measure the Iload while the load is an square wave oscillator or something so?!

 

[dr.power]

There are lots of comprimises in electronics design.

It should be fine, ground loops are not a big problem in a power supply.

Thanks.

I am sure that the circuit will work great if I do not filp one regulator chip too.

I would like to know if the read square in the pic of my other post (post #15) is generating any ground loop?
Why the ground loops are not problematic in a power supply plz?

 

[dr.power]

Hi and thank.

Zipped files are compressed files. When unzipping the original files are being restored (in that case the schematic and board files).

yes you are right, but I told that I am not able to open them in proteus software.

I used screw head terminals with a pin distance of 5.08mm (0.2")

What is the name for it in the software plz? I would like to search for it in the proteus.

I never use Proteus ARES to create a PCB. It has a very limited library for components. Instead I use Eagle.
Proteus ARES should offer a function called "Restrict" or "Keepout". Use the center of the mounting drill hole and draw a circle around it using the "Restrict" layer. The ground pour should then stop at the "border". Clearances are 0.4064mm (0.016"). Board size is 66.5X42.0mm (2.62X1.65")

Yea, proteus has a function called keepout. But I thought that you have used aready package or a footprint to for the screw's....

Boncuk[/QUOTE]